In general, it is possible to provide a decorative polychromatic multilayer film made of laminated metal layers that provides rainbow colors and a pleasing appearance; however, these decorate layers interfere with electromagnetic (EM) transmissions used in communication devices, and in addition exhibit inferior abrasion resistance. Therefore, such decorations are limited to use in casings or parts of a mobile phone or other electric device that do not in require abrasion resistance.
In the prior art decorating method, microparticles of glass and metal are admixed into a coating material, and exhibit diffuse reflections. However, the particles settle during application because of the different specific gravities between the coating material and the microparticles.
Thus, several processes for making a laminate have been considered. For instance, in a method that substantially excludes the use of microparticles, an under coat forming composition substantially free of rainbow colored (i.e., iridescent) microparticles is coated onto a base material and hardened; then, a thin metal film is formed on the hardened layer, thereby producing an iridescent laminate having a metal layer with an irregular surface. The coating composition comprises urethane methacrylate, a compound having one or more intra-molecular radical polymeric double bonds, and a photopolymerization initiator (as described in JP 2007-54827); or in an iridescent transfer film, of which a release layer, a protective layer, and an iridescent layer with a high refractive index are formed on both sides of a low refractive index film, and an adhesive layer is formed sequentially on one side of a plastic film, a high refractive index film on at least one side of the metal film and is formed on the low refractive index film (as described in JP 2003-326895); or a decorative plastic 10 is mounted on resin plastic with multiple layered laminate films 12, which selectively reflects visible light at specific wavelengths, thereby providing iridescence. The multiple layered laminate film 12 is formed by alternatively laminating a first resin film as a first layer 12a, and onto which a second resin film as a second layer 12b, integrating at least eleven layers (as described in JP 2006-216493).
However, the laminate as described in JP 2007-54827 and JP 2003-326895 adversely affect EM transmissions of devices onto which it is mounted because of the existence of the metal film in the laminate. Additionally, the production of the laminate as described in JP 2006-216493 having at least eleven layers of resin with different refractive indices is complicated and time-consuming.